The present invention relates to a recording medium cartridge of the type which includes a memory for storing information concerning signals recorded on the recording medium and more particularly, although not exclusively, relates to a method for recording information on the memory so as to improve the efficiency of retrieving information stored on the recording medium.
In order to store digital electronic data, it is known to use magnetic tape data cartridges which are inserted into a tape drive unit having a plurality of read/write heads. Typically such magnetic tape storage devices may be used to back up data generated by a host device, eg. a computer.
In order to improve ease of access to data recorded on tape, it is known to include a solid state memory device within the cartridge and to store in this memory information relating to, for example, a listing of the contents of the tape.
In particular, in EP 0,646,914, there is realized an analog data recording video cassette of the type in which data is recorded in a plurality of scans across a width of the tape by a rotating record head, and which includes a memory device which can be configured to store fundamental information concerning the cassette and its contents, such as table of contents information or the like. In EP 0,646,914, the information concerning the cassette and its contents is transferred from a VCR tape drive unit to the video cassette through a set of metallic terminals provided on the cassette which make electrical and physical contact with a corresponding set of metallic terminals on the VCR drive unit.
In EP 0,580,434, there is disclosed a VCR recording medium cartridge, wherein video data is stored in a plurality of diagonal scan passes across a width of the tape, by a rotating write head, and which includes a memory circuit for storing information concerning signals recorded on the recording medium within the cartridge. At least some of the data stored within the memory circuit can include the starting and ending positions of signals recorded on the recording medium and these starting and ending positions are recorded in the memory circuit at substantially the same time as recording to the recording medium. However, in EP 0,580,434 using an EEPROM memory, long write times are encountered, whereas use of a flash memory leads to long accessing times.
In WO 89/10615, there is disclosed a cassette containing a recording medium for use storing computer generated data, which includes a storage device for storing directory information concerning the contents of the tape. The storage device comprises a non-volatile random access memory and associated microprocessor and is accessed by either inductive coupling or electrical contact pads.
In U.S. Pat. No. 4,338,644 there is disclosed a cassette containing a recording medium which also includes within the housing an electronic memory and semiconductor circuits for storing data relating to the cassette or tape therein.
EP 0,640,972 discloses a video tape cassette containing memory device which can be used to store information concerning the contents of the information recorded on the video tape, such as time of recording, position and the like.
In order to facilitate accessing data recorded on tape and to protect against accidentally overwriting essential data when recording new data it is known to record a marker on tape signifying the position of the last valid user data on the tape (EOD). It is also known to record the position of the EOD in a special reserved area of tape whose position is defined by the particular format of that tape. However, it is necessary to read this area of tape when the cartridge is first loaded and to re-record this area with the latest EOD position when the cartridge is unloaded. This repeated winding and rewinding of the tape each time new data is recorded to the tape adds significantly to the time required to back up data from a host device. In addition, wear on the tape caused by repeated winding forwards and backwards results in a decrease in reliability.
As data recording technology develops and the density of data written onto tapes increases it becomes increasingly imperative to improve both data access times and tape reliability.
The specific embodiments and methods according to the present invention aim to improve the accessing of data written in high data density data tape systems having a plurality of read/write heads. The specific embodiments and methods disclosed herein aim to provide improved protection against loss of data resulting from unplanned power loss to two such devices during data back up.
Specific methods according to the present invention, recognize that if a record of the position of the last recorded data on tape is stored in a memory device, then the current position of the last recorded data on a tape can always be retrieved.
According to a first aspect of the present invention there is provided a data storage device (200) comprising: a casing (200); a data storage medium (100) for storing data; and a memory device (416), wherein said memory device (416) is configured to store data identifying a location of a last stored data written onto said data storage medium (100); and data defining an end of said stored data (114) is recorded on said data storage medium (100), characterised in that said data, identifying a location of said last stored data (114), is stored in said memory device (416) before said data defining end of stored data (114) is recorded on said data storage medium (100).
In the best mode, said data storage medium comprises an elongate tape (100) and said write operation comprises a write pass along a length of said tape.
Said write operation may comprise a write traversal along a length of said tape.
Preferably, said memory device comprises: a memory area (416); a means (410) for writing data into said memory area (416); and a means (410) for reading said data from said memory area (416).
The memory area preferably comprises an area of an electrically erasable programmable read only memory, and the means for writing data into the memory area preferably comprises a processor adapted to receive data from a receiver device, the whole arrangement being powered by an inductive signal being produced by a corresponding transmitter device in a tape drive device to which the data storage device is placed in close physical proximity to during normal read/write operations of data to the data storage medium. The means for reading data from the memory area preferably comprises said processor, configured to read from said memory area. The processor is preferably connected to a transmitter which is capable of transmitting data stored in the memory area away from the data storage device, to a corresponding transceiver mounted in a tape drive device. The memory area, processor, transmitter and receiver, together with a crystal oscillator, and an aerial form a transponder device which is physically mounted on a casing of the data storage device. The transponder is inductively powered by RF signals produced by a corresponding transceiver mounted on the tape drive device, which both powers the transponder, and communicates with the transponder via the RF link.
Preferably said data storage medium comprises a magnetic tape data storage system.
According to a second aspect of the present invention there is provided a data recording apparatus comprising: a means for writing data (110, 120) to a data storage medium (100); a means for reading said data (110, 120) from said data storage medium (100); characterised by comprising: a means for writing data (400) identifying a position of a last user data written onto said data storage medium in a memory device, wherein said data recording apparatus operates to write to said memory device said data identifying a position of a last user data, before terminating a write operation of writing data to said data storage medium.
The data recording apparatus preferably comprises a transceiver as hereinabove described, mounted in a tape drive device. The transceiver comprises a transmitter, a receiver, a crystal oscillator, a processor, a serial interface, and an antenna. The antenna of the data recording apparatus communicates with the antenna of the data storage device, and is arranged to inductively power the data storage device by means of RF signals transmitted by the transmitter.
According to a third aspect of the present invention there is provided a method of writing data to a data storage medium said method comprising the steps: formatting data into data sets; performing a write operation to write said data sets to a plurality of tracks (110, 120) of said data storage medium (100); and writing a last data set to said plurality of tracks, of said data storage medium (100), characterised in that said last data set (114) contains information concerning a location of said last data set on said data storage medium (100); and said information concerning a location of said last data set of said data storage medium (100) is written to a memory device (416) before said information is written to said data storage medium (100).
Preferably, said information concerning a location of said last data set of said data storage medium is selected from the set: tape write pass for last written EOD (601); load count (602); record count at EOD (603); file mark count at EOD (604); EOD data set number (605); wrap section number of EOD (606); validity of EOD (607); first CQ set number (608); physical position of EOD (609); reserved; and a cyclical redundancy code to verify a correct location of an EOD (611).
According to a third aspect of the present invention there is provided a method of operating a tape data storage device, comprising a tape data storage medium and an associated quick access memory unit having an average access time of less then an average access time of said tape data storage medium, said method comprising the steps of: storing in said quick access memory unit (416) location data describing a location of a most recently written end of data recorded on said tape data storage medium, said location data identifying a physical position of said most recent end of data (114) in relation to said tape, wherein said location data is stored in said quick access memory unit before terminating a write operation writing said recorded data to said tape data storage medium.
Preferably said location data comprises data identifying a longitudinal position along a length of said tape, and a position across a width of said tape.
Preferably said location data is first stored in said quick access memory unit, and is subsequently stored on said tape.
According to a fourth aspect of the present invention there is provided a method of writing data to a data storage medium said method characterised by comprising the steps of: formatting said data into a plurality of data sets; performing a write operation to write at least one data set of said plurality of data sets to at least one track of said data storage medium (100); reading at least one said data set from said data storage medium (100); verifying that said read data set has been successfully written to said data storage medium; and storing data in a memory device (416), said data identifying a location on said data storage medium of said successfully written data set.
Preferably said data identifying a physical location on said data storage medium of said successfully written data set is selected from the set: tape write pass for said successfully written data set; load count (602); record count at said successfully written data set; file mark count at said successfully written data set; said successfully written data set number (605); wrap section number of said successfully written data set; validity of said successfully written data set; first CQ set number (608); physical position of said successfully written data set; and a cyclical redundancy code to verify a correct location of said successfully written data set.
Preferably said steps of reading at least one data set; verifying that said read data set has been successfully written; and storing in a memory device said data identifying a location of said successfully written data set, are periodically repeated during a data write operation comprising writing a plurality of said data sets to said data storage medium.
Preferably said data identifying a location of a successfully written data set is stored in said memory device at least once for every write traversal of said data storage medium.
Preferably said data identifying a location of said successfully written data set comprises data describing a logical position of said successfully written data set.
Preferably said data storage medium comprises an elongate tape, and said data identifying a location on said data storage medium comprises data identifying a longitudinal position along a length of said tape, and a position across a width of said tape.
In the best mode, the memory device is physically associated with the data storage medium. Suitably, the memory device comprises an electrically erasable programmable read only memory.
According to a fifth aspect of the present invention there is provided a data storage device (200) comprising: a data storage medium (100) for storing data; and a memory device (416), characterised in that: said memory device (416) is configured to store data identifying a location of a last successfully written set of data stored on said data storage medium (100).
According to a sixth aspect of the present invention there is provided a data recording apparatus comprising: means for writing data (110, 120) to a data storage medium (100); means for reading said data (110, 120) from said data storage medium (100); characterised by comprising: means for writing data identifying a position of a last user data written onto said data storage medium, said means for writing data adapted for writing said data to a memory device associated with said data storage medium, wherein said means for writing said position identifying data operates to write data identifying a location on said data storage medium of a successfully written data set.
Preferably said data recording apparatus further operates to read from said data storage medium a most recently read data set written to said data storage medium; and verify that said most recently read data set is successfully written.